Nowadays, with rapid progress in science and technology, more and more electronic apparatuses such as medical devices and servers need electricity supplied by Uninterrupted Power Supplies (UPSs). However, UPSs are usually expensive, and particularly, are not suitable for situations of low power requirements. Thus, it is quite necessary to devise novel, general purpose UPSs with high reliability, high efficiency and low cost.
FIG. 1 depicts a circuit block diagram of a redundant power supply system in conventional technologies. The system includes two Alternating Current (AC) sources 11a and 11b and two Alternating Current to Direct Current (AC/DC) conversion modules 12a and 12b. Output terminals of the two AC/DC conversion modules 12a and 12b are connected in parallel through diodes D1 and D2, thereby supplying electricity to a final load 13. In this power supply system, reliable operations of the load 13 may be guaranteed as long as any one of the input power supplies can supply electricity.
However, this redundant power supply system necessarily has two AC/DC conversion modules 12a and 12b, and the cost of an AC/DC conversion module is relatively higher than other components in a power supply system, and thus the whole cost of the power supply system rises.
Furthermore, each AC/DC conversion module has to be designed based on the maximum power required by the load 13, so as to guarantee that the load 13 may be supplied with the maximum power when only one input is available (e.g., one of the AC sources has a failure such as power off). This involves in more space for the power supply system and causes an increase in the cost of the power supply system.